Primarys and secondarys.. How?

[John S Gwynne]

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From: Craig Pugsley <c.pugsley at trl.oz.au>
Message-Id: <199504060704.AA25262 at shiva.trl.OZ.AU>
Subject: Re: Primarys and secondarys.. How?
To: r.dingli at ee.mu.oz.au (robert dingli)
Date: Thu, 6 Apr 1995 17:04:38 +1000 (EST)
Cc: DIY_EFI
In-Reply-To: <199504051042.UAA13966 at mullian.ee.mu.OZ.AU> from "robert dingli" a
t Apr 5, 95 08:42:24 pm
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> Craig asks,
> > 
> > With an engine with a primary and secondary stage, do you need different
> > fuel curves for the primary and secondary (IE in a Mazda rotary, where
> > the primary and secondary have different port timing (~= two intake
> > valves in a piston engine following different cam profiles).
> 
> First, some background ..
> 
> Rotaries tend to have rather peculiar fuelling requirements. 
> While parallel injection once per revolution works fine in a piston engine, 
> we found that it resulted in unequal fuelling for a rotary.  Each rotor 
> draws in air every revolution, 180 deg out of phase of the other, and produce
s
> relatively large pressure pulsations in the intake manifold.  As a result
> the fuel has the be injected either twice per revolution or sequentially. 
> We settled on sequential injection for the primaries to avoid injector 
> cut-off problems near idle and the larger non-linearity in fuel flow near 
> 100% duty cycle.  The single secondary output (which is used on only a 
> fraction of applications) injects twice as often to provide equal fuelling.

Egads! sounds complicated. Injecting twice per revolution at high RPM
could get a bit dicey.

I presume if it's in a situation like mild primarys (eg stock/extend)
and bridge or J secondarys that you could use MAP for the primarys and
throttle position for the secondarys (Ie with the 4 barrell setup).
(Or would the vacuum fluctuation be too wild in the primarys? -
nessecitating 2 Throttle position sensors or using mechanical secondarys
and taking the single TPS as your only load input)

I thought it would be a nice idea to use petrol (gasoline) in the
primarys and methanol in the secondarys for more power.
A freind is about to try this idea on his carbed car, as the
primary and secondary float bowls - I'll report on the outcome.

> As for fuel curves, the speed density mapping is calibrated empirically.

I love that bit - makes tuning lots easier.

Cheers,
Craig.